Bitbucket is free for private repos if there are <=5 contributors (unless you have a .edu email = unlimited free).

GitHub also provides free private accounts to .edu addresses: https://education.github.com/discount_requests/new

(And non-profits: https://github.com/nonprofit)

BitBucket is free for private repos with less than five people. Doesn't work for a lot of businesses, which is where most of the money is.

..but if they didn't charge what does it matter that it's where the money is?

Because when your team gets to 6 people, you A) have money (hopefully) and B) your code is already in BitBucket, so choosing to pay them over GitHub is a no brainer.